audio-settings: Fix unneeded async for GetProperties

GetProperties method call for Audio settings returns the reply in the
same iteraction, it doesn't need to be asynchronous.
include: Add handsfree card create / remove API
handsfree-audio: Implement card create / remove
include: Add handsfree card register method
handsfree-audio: Don't hardcode '/' path

Use OFONO_MANAGER_PATH instead
handsfree-audio: Add skeleton D-Bus registration

For HandsfreeAudioCard objects
handsfree-audio: Unregister from DBus on removal
handsfree-audio: Implement card GetProperties
handsfree-audio: Implement the GetCards method
handsfree-audio: Implement CardAdded signal
handsfree-audio: Impelement CardRemoved signal
bluez4: Increase Bluez 4 D-Bus timeouts to 60 seconds

RequestAuthorization method call may trigger pairing and/or pop up a
dialog in the remote device to which the user needs to react. Thus
increase D-Bus timeouts to 60 seconds for the Bluez 4 plugin.
doc: Add possible handsfree-audio API errors

This patch adds possible errors that can be returned by Register and
Unregister methods of the Manager interface.
handsfree-audio: properly increment next_card_id
hfp_hf_bluez5: Add registering Audio Card

This patch registers the Handsfree Audio Card when the service level
connection is established.
hfp_hf_bluez5: Add local address to Audio Card
hfp_hf_bluez5: Remove Card when SLC fails

This patch removes the previously created Audio Card if the service
level negotiation fails.
hfp_hf_bluez5: Remove Card if SLC is disconnected

This patch removes previous registered Audio Card when the remote
Bluetooth device triggers the service level disconnection.
hfp_hf_bluez5: Remove Card when modem is disabled
hfp_hf_bluez5: Remove Card on RequestDisconnection

For local initiated disconnection the GAtChat disconnect callback is not
called. For this case, Audio Card remove function needs to be called.